Construction of Ecological Corridors in Karst Areas Based on Ecological Sensitivity and Ecological Service Value

Abstract

Ecological corridors play a key role in promoting the flow of ecological processes, guaranteeing ecological function services and maintaining biodiversity. Based on ecological sensitivity and ecological service values, ecological corridors in typical karst areas of Ningyuan County were constructed to lay the foundation for ecological environmental protection and land development and utilization in the county. Based on the current land use situation in 2020, the ecological source sites were identified by the combined results of ecological sensitivity evaluation and ecosystem service value analysis, and then potential corridors were generated based on the minimum cumulative resistance model (MCR) and the minimum cost path method, and key corridors were identified by the gravity model. The results show that (1) the areas exhibiting strong sensitivity are concentrated within regions characterized by better ecological environment quality; the ecosystem service value and ecological sensitivity have a similar distribution pattern, and those with high ecological value are mainly distributed in areas with better habitat quality such as woodlands and along water systems. (2) The total area of ecological source land in Ningyuan County is 879.14 km², accounting for 35.15% of the county area, mainly distributed in the south and north of the county. (3) There are nine ecological corridors in Ningyuan County, which are radially distributed in a spider-web manner, five important ecological corridors and four general ecological corridors, with total lengths of 96 km and 120.87 km, respectively.

1. Introduction

With the rapid progress of urbanization, ecological and environmental problems are becoming increasingly prominent, thus ensuring the safety of ecosystems has become a guiding principle in the exploitation of resources under the context of ecological civilization construction [1]. The ecological corridor, as one of the most essential research objects in the ecological security pattern construction, has attracted great attention and continuous exploration. The ecological corridor has some additional ecological functions compared to ordinary corridors and is equipped with ecological roles such as biodiversity protection, filtration of pollutants, reduction in soil erosion, and control of rainwater flooding [2]. In addition to ecological benefits, ecological corridors also have the role of maintaining the integrity of the region and passing on cultural heritage. Yuan et al. take the ancient capital of Luoyang as an example of connecting cultural heritage on the basis of ecological corridors in order to protect the special value of our heritage resources in a more complete way [3]. The inter-regional connectivity of ecological corridors can promote the migration of organisms between fragmented patches and increase the gene flow between populations, thus reducing the fragmentation of regional habitats, and the construction of ecological corridors has greatly alleviated the environmental problems now facing regional development. For example, Albert et al. used land-use change simulations to explore robustness of habitat networks and assessed the contribution of habitat fragmentation to regional habitat network connectivity in a suburb of Montreal, Canada, using 14 vertebrate species [4]. Jalkanen et al. showed how to identify good ecological networks in Uusimaa province through zoning and to assess the expected connectivity effects of regional planning, informing regional planning [5]. The 19th National Congress of the Party has clearly proposed to elevate the construction of ecological civilization to a “millennium plan” and put forward the requirements of protecting the ecological environment, building ecological corridors and improving the quality and stability of the ecosystem in this meeting.

Ecological corridors have been studied by authors since the 20th century, and many countries have made continuous progress in the conservation of biological habitats. However, studies have shown that the habitats of many animals are fragmented and disconnected from each other, a phenomenon that threatens the survival of plants and animals [6,7]. In the 1990s, Forman proposed the “patch-corridor-substrate” model principle, and corridors were used as an important indicator in ecological spatial planning [8]. In 2008, Henny studied the corridors in the Green River basin in the Netherlands, and the results showed that corridors are a bridge between science and politics [9]. In the 21st century, the ecological corridor network systems in the United States and Europe have been studied in urban ecological planning using the theory of landscape ecology and the model of “patch, corridor, matrix”. The study of ecological corridors in China is relatively late, and the scale of corridor construction is mostly on a relatively large scale, such as provincial, municipal, and watershed [10,11,12].

As the basis for building ecological corridor systems, ecological source sites [13] are important patches that provide ecological service functions and are of great value to ecological security. Therefore, ecological source sites need to be identified and determined by a scientific and comprehensive approach, which is worth exploring in depth. In past studies, a common way is to directly select green areas, forest parks, or nature reserves with high ecological service value and more fragile ecology as ecological source sites [14,15]; for instance, Li Hui et al. [14] selected five nature reserves and scenic spots as ecological source sites and analyzed them with two factors of surface landscape type, slope, and corresponding resistance factor coefficients to construct a landscape security pattern. Kang-Li Wu et al. [15] selected existing species habitats and important landscape elements such as groves and green campuses as priority strategic points for ecological corridor construction in the study area to provide strategies for ecological corridor planning. This identification approach is more one-sided, with the disadvantage that it is highly subjective and difficult to reflect the linkages among ecosystems. In recent years, morphological spatial pattern analysis methods [16] have been introduced to identify ecological source sites in ecological networks; for instance, Yu-jie Wang et al. [17] used morphological spatial pattern analysis (MSPA) to identify urban core areas and existing corridors to study ecological safety in densely populated areas. However, the existing identification methods pay less attention to the ecosystem condition of the parcel, and the method system of source-site identification has not been formed for different landforms. Only by scientifically evaluating the ecological environment and service functions can we reasonably construct the county ecological security pattern, focusing on quantifying the ecosystem condition such as ecological sensitivity and ecosystem services: (1) ecological environmental sensitivity is used to reflect the ecosystem’s response to human activity disturbance and natural environmental changes, as a way to indicate the ease, likelihood, and recovery rate of ecological and environmental problems in the region [18,19]. Its results are mainly used to guide urban development [20], ecological environmental protection and construction [21], ecological protection red line delineation [22], and the evaluation of the carrying capacity of national land resources and suitability of national land space development [23]. (2) Ecosystem services refer to the benefits obtained by humans directly or indirectly from ecosystem functions, including those obtained from products and services [24,25]. At present, a large number of results have been achieved in the research of ecosystem service values at home and abroad, which are mainly applied in the study of landscape pattern evolution [26], ecological compensation standard design [27], and ecological function area protection [28]. There are fewer studies to determine ecological source sites by combining ecological sensitivity and ecosystem service value, and it is scientific to determine their ecological value by combining the two to screen out ecologically important plots in karst areas where the landscape is complex and a single identification method is prone to error.

The results of ecological corridor construction are relatively abundant, but the research is mostly based on macro-theoretical analysis and lacks practical research from the county planning level, which makes it difficult to identify resource and environmental advantages and shortcomings in the ecological planning process. In China, the contradiction between humans and land is prominent, and the karst region has a low environmental capacity and a more fragile environment than the normal mountain areas [29]. Few studies have been conducted on its spatial correlation and connectivity with respect to ecological vulnerability characteristics, and ensuring ecological sustainability in karst regions is critical. The original large-scale traffic artery division of natural ecological space in Ningyuan County has led to the obstruction of material circulation and energy exchange between ecosystems, serious fragmentation of ecological space and damage to the integrity of ecosystem functions. The county, as the fundamental administrative unit of China, is facing an urgent need for effective measures to address the challenges related to regional ecological protection and development.

In order to reduce the fragmentation of natural areas caused by urbanization, agriculture, and industrial development, and to strengthen the integrity and connectivity of ecosystems, it is necessary to study the construction of regional ecological corridors. This study takes Ningyuan County, a typical karst region, as the study area, adopts ecological sensitivity and ecological service value to identify ecological source sites, constructs an ecological corridor system in Ningyuan County based on the minimum cumulative resistance model type, lays the foundation for ecological environmental protection and land development and utilization in the county, and provides a reference for the formulation of reasonable regional environmental management policies.

2. Materials and Methods

2.1. Study Area

Ningyuan County is in the south of Yongzhou City, Hunan Province, southeastern China, between 110°42′~112°27′ E and 25°11′~26°08′ W. It is near Xintian County, Jiahe County, and Lanshan County in the east, Dao County and Shuangpai County in the west, Jianghua Yao Autonomous County in the south, and Qiyang County in the north, with a length of 104.7 km from north to south and a width of 52.2 km from east to west, and a total land area of about 250,146.21 hm² (Figure 1).

Ningyuan County has a warm climate, abundant rainfall, a developed water system, and dense river network, and is known as a “natural greenhouse”. It is a typical karst area, surrounded by mountains on all sides, with the shape of a boat, an altitude range of 97 to 1941 m, a wide mountainous area, many land types, good soil quality, significant vertical zonal differences, and great development potential. Due to the fragmentation of natural areas caused by urbanization, agricultural and industrial development, ecosystem integrity and connectivity need to be strengthened, and the wildlife habitat and breeding environments are affected. The safety network for biodiversity conservation needs to be improved urgently. For example, the government can designate ecological protection red lines and carry out biodiversity observation at ecological source sites.

2.2. Data Sources

The vegetation cover information was calculated using Landsat 8 OLI remote sensing images using the GEE platform. The elevation, slope, and river were extracted from the DEM digital elevation data of ASTER GDEM in Ningyuan County. DEM image maps of Ningyuan County were derived from Geospatial Data Cloud (http://www.gscloud.cn/search (accessed on 1 June 2022)). The data on the current status of land use were derived from the GlobeLand30 global public geographic information platform (http://www.globallandcover.com/ (accessed on 1 June 2022)). Road spatial data were obtained from the Resource and Environmental Science and Data Center of the Chinese Academy of Sciences (https://www.resdc.cn (accessed on 1 December 2022)). Soil was derived from the second soil survey of China in 1986. Rainfall was obtained from National Meteorological Information Center (https://data.cma.cn/ (accessed on 1 December 2022)). The time nodes of the above unspecified data were all in 2020, converted into grid format with a resolution of 30 m. The socio-economic data were derived from the Statistical Bulletin of National Economic and Social Development of Ningyuan County in 2021.

2.3. Ecological Sensitivity Evaluation Model and Index System

2.3.1. Evaluation Model

With the spatial analysis technology of remote sensing interpretation and GIS, the method of combining single-factor evaluation analysis and multi-factor comprehensive evaluation analysis was used to construct an ecological sensitivity evaluation index system reflecting the ecological sensitivity of land in Ningyuan County and classify and evaluate the level of single factors through reclassification; second, the weight of each factor was determined by the entropy value method [30], and the ecological sensitivity level of comprehensive factors in Ningyuan County was obtained through superposition analysis to complete the sensitivity analysis of various ecological environmental problems and clarify the overall situation and spatial distribution characteristics of regional ecological sensitivity.

The model equation is as follows:

$$S_k={{\displaystyle \sum }}_{i=1}^n{W}_i\times X_k\left(i\right)$$

(1)

where k denotes the $k$-th evaluation unit, $i$ denotes the $i$-th evaluation factor, $n$ is the total number of evaluation factors, $S_k$ is the combined value of the $k$-th evaluation unit, $W_i$ is the weight of the i-th evaluation factor, and $X_k\left(i\right)$ is the sensitivity evaluation value of the $i$-th evaluation factor of the $k$-th evaluation unit.

2.3.2. Indicator System

Due to the high degree of complexity of the ecosystem, there are no fixed criteria for the selection of ecological sensitivity factors. Different study areas should analyze their differences according to the ecological environment in the field and select each ecological sensitivity factor that best reflects the region [29]. According to the research needs and combined with the characteristics of its karst mountainous area, vegetation cover, slope, and land use type were selected as natural geographic attributes to reflect the current situation and stability of land use in Ningyuan County; the degree of influence of human activities on the ecological environment can well reflect the sensitivity of the ecosystem; therefore, factors such as the population density, GDP, and distance from roads were selected as socioeconomic attributes to reflect the sensitivity of the land to human activities. They are a side view of the level of human activity in the region. Areas with high human activity are less susceptible to environmental impacts, and relatively low ecological sensitivity. The degree of soil erosion and distance from rivers can reflect the ecological environment of the region, and soil erosion is a typical ecological problem in karst areas. The soil erosion degree level is classified according to SL190-2007 “Soil Erosion Classification and Grading Standard” issued by the Ministry of Water Resources of China. In this paper, eight factors are selected as the main sensitivity factors of the study area, and the corresponding evaluation index system is constructed. With reference to the research results of several authors [31], the influence levels of each factor on the ecological sensitivity of land were divided into four levels according to the importance of each ecosystem influence factor within Ningyuan County, namely, insensitivity, low sensitivity, moderate sensitivity, and high sensitivity, and assigned values 1, 3, 5, and 7 for quantification, respectively (

Table 1. Ecological environment sensitivity evaluation system.

Evaluation Factor Type	Evaluation Factors	Weights	Insensitivity	Low Sensitivity	Moderate Sensitivity	High Sensitivity
Physical Geographic Attributes	Vegetation cover	0.1898	>0.7	0.5–0.7	0.3–0.5	<0.3
	Slope (°)	0.1636	<5	5–20	20–35	>35
	Land Use Type	0.0609	Construction land	Cultivated land	Grassland	Woodlands, Waters
Socio-economic attributes	Population density (persons/km²)	0.0223	>400	300–400	200–300	<200
	GDP (CNY million/km²)	0.0129	>1500	1000–1500	500–1000	<500
	Distance from road (m)	0.1407	<1000	1000–2000	2000–3000	>3000
Ecological attributes	Degree of soil erosion	0.1720	Level 1	Level 2	Level 3–4	Level 5–6
	Distance from river (m)	0.2378	>500	200–500	100–200	<100
-	Assignment	-	1	3	5	7

).

2.4. Ecosystem Service Value Calculation

This paper adopts the improved ecosystem service valorization method based on the unit area value equivalent factor proposed by Xie Heights et al. [32] for ESV assessment, as in Equations (2) and (3). Considering the actual situation of land use types in Ningyuan County, this paper adjusts to the ESV calculation index: the ESV index of cropland calculated by weighting the ratio of paddy field to dryland area in the Statistical Yearbook of Ningyuan County in 2021. The ESV indicators for each land use type in Ningyuan County are shown in

Table 2. Ecosystem service value coefficient per unit area of Ningyuan County.

Ecosystem Function	Cultivated Land	Woodland	Grassland	Waters	Construction Land
Gas regulation	436.58	941.52	854.74	334.09	0.00
Climate regulation	225.82	2820.21	2260.50	993.58	0.00
Purifying the environment	66.60	837.38	746.27	2408.02	0.00
Water harvesting	929.46	2056.58	1657.41	44,359.69	0.00
Soil conservation	108.71	1149.78	1041.31	403.51	0.00
Maintaining nutrient circulation	75.27	86.78	78.10	30.37	0.00
Biodiversity conservation	82.93	1045.65	945.85	1106.39	0.00
Food production	537.89	125.82	164.87	347.10	0.00
Raw materials	70.77	286.36	242.97	99.79	0.00
Aesthetic landscape	35.98	459.91	416.52	820.03	0.00
Total value	2570.01	9809.98	8408.56	50,902.57	0.00

.

$$ESV={{\displaystyle \sum }}_{i=1}^{n}V{C}_i\times A_i$$

(2)

where $ESV$ is the total value of annual ecosystem service value in the study area, $V{C}_i$ is the ecosystem service value per unit area of the $i$-th land use type (USD/hm²), $A_i$ is the area of the $i$-th land use type, and $n$ is the number of types of land use types.

$$ES{V}_f={{\displaystyle \sum }}_{i=1}^{n}V{C}_{fi}\times A_i$$

(3)

where $ES{V}_f$ is the total value of annual ecosystem service value in the study area and $V{C}_{fi}$ is the service value per unit area (USD/hm²) of the $i$-th land use type corresponding to the $f$-th ecosystem function.

2.5. Ecological Corridor Model Construction

In this paper, the minimum cumulative resistance model ($MCR$) is used to extract the corridors between ecological sources [33,34]. The $MCR$ model considers the source, distance, and landscape interface characteristics to calculate the minimum cost required for the movement of species from the source to the destination. The basic equation is as follows:

$$MCR=f_{min}{{\displaystyle \sum }}_{j=n}^{i=m}\left(D_{ij}\times R_i\right)$$

(4)

where $D_{ij}$ is the distance from ecological source point $j$ to spatial unit $i$ and $R_i$ is the resistance coefficient of spatial unit $i$.

The key to the establishment of the MCR model is the selection of the source [35] and the construction of the resistance surface system [36]. By referring to the relevant literature and research results [16,37,38], the resistance evaluation system was constructed by selecting factors such as the land use type, elevation, slope, and NDVI, as shown in

Table 3. Ningyuan resistance factor assignment.

Resistance Factor	Tiered Metrics	Resistance Factor
Land Use Type	Woodland	1
	Grassland	40
	Waters	30
	Cultivated land	50
	Construction Land	100
Elevation factor (m)	<300	10
	300–500	20
	500–800	30
	>800	50
Slope factor (°)	<5	10
	5–15	20
	15–25	30
	>25	50
NDVI	>0.8	10
	0.7–0.8	20
	0.6–0.7	30
	<0.6	50

, and the higher the score indicates the greater the resistance in the biological migration process.

3. Results

3.1. Ecological Sensitivity Evaluation and Ecological Service Value

3.1.1. Ecological Sensitivity Evaluation

On the whole, the ecological sensitivity of Ningyuan County is high, but locally, the degree of ecological sensitivity varies slightly in different areas (Figure 2). The highly sensitive ecological environment areas in Ningyuan County are mainly located in the northwestern and southern parts of the county, including the townships of Jiuyi, Mianhuaping, Qingshuiqiao, Shuishi, Tongmuluo, Wanjing, Wulongshan, and Zhonghe. From the comprehensive evaluation results in

Table 4. Comprehensive assessment results of ecological sensitivity.

	Insensitivity	Low Sensitivity	Moderate Sensitivity	High Sensitivity
Area (km2)	646.13	895.77	762.45	197.12
Proportion (%)	25.83	35.81	30.48	7.88

, we can see that the degree of ecological sensitivity in the county is generally low, and the area of low sensitivity and moderate sensitivity is large, with an area of about 895.77 km² and 762.45 km², accounting for 35.81% and 30.48%, respectively. Being in a typical karst area, karst landscapes are spread all over the county area, and vegetation on such terrain has a poor ability to contain water because of regular soil erosion, a shallow soil layer, and loose soil quality. The ecological environment is less able to resist interference from external factors, and the ecological environment itself is more fragile. The ecological sensitivity itself is a comprehensive ecological environment problem in karst mountainous areas. For the moderately sensitive areas, their ecological environment is also more fragile and can be properly developed, but the development should follow the principle of integration of protection and development and also actively prevent ecological environment damage.

3.1.2. Value of Ecological Services

The total value of ecosystem services in Ningyuan County in 2021 is USD 2862.47 million. The natural breakpoint method [39] was used to classify the ecosystem service values within the study area into four classes, with the low-value area of USD 17,010–48,420/hm², the medium-value area of USD 48,420–65,280/hm², the high-value area of USD 65,280–82,590/hm², and the extreme-value area of USD 82,590–136,390/hm². As can be seen from the

Table 5. Distribution of ecosystem service value levels in Ningyuan County.

	Low-Value Area	Median-Value Area	High-Value Area	Extreme-Value Area
Area (km2)	385.48	574.09	708.66	833.99
Proportion (%)	15.41	22.95	28.33	33.30

, the overall condition of ecosystem service value in Ningyuan County is good, with most of the areas being high value and above. Among them, the extreme-value area covers 833.99 km², accounting for the largest proportion of 33.3%; only 385.48 km² is low-value area, accounting for 15.41%. As can be seen from Figure 3, the distribution of ecosystem service value and ecological sensitivity in Ningyuan County has similar characteristics: the southern and northern parts of Ningyuan county are higher than the central parts, and the western parts are higher than the eastern parts. The extreme-value ecosystem services in Ningyuan County are concentrated in Wulongshan, Tongmuluo, Mianhuaping, Zhonghe, Shuishi, and Jiuyi, mainly because these are the concentrated distribution areas of woodland and water area, which provide the highest value of ecosystem service per unit area. The areas with low-value ecosystem services coincide with the distribution of construction land in established towns, rural settlements, transportation, and mining, because construction land provides less or no value to ecosystem services and even brings negative impacts.

3.2. Ecological Corridor Construction

According to the “inverse barrel principle”, i.e., that the score of ecological importance is the same as the highest score in ecological sensitivity and ecosystem service value, the ecological sensitivity evaluation grading map and the ecosystem service value distribution map are superimposed by the maximum value using the meta-statistical tool (

Table 6. Ecological importance hierarchy of Ningyuan County.

Ecological Sensitivity Level	Ecological Service Value Rating	Score	Ecological Importance Level	Area (km²)
Insensitivity	Low-Value Area	1	IV	200.54
Low sensitivity	Median-Value Area	2	III	578.74
Moderate Sensitivity	High-Value Area	3	II	815.80
High Sensitivity	Extreme-Value Area	4	I	918.33

) to obtain the ecological importance grading distribution map of Ningyuan County.

The higher the ecological importance level is, the stronger the urgency of needing protection. Level 3 and 4 are areas that do not need protection for the time being, including construction land in established towns, rural settlements, transportation, and mining. Level 2 is the area that needs protection, mostly arable land or grassland, and Level 1 is the priority protection area mainly for forest land and water. Six patches are extracted from the Level 1 area by merging adjacent patches as ecological source areas with a total area of 879.14 km², as shown in Figure 4 and Figure 5, and the ecological corridor of Ningyuan County is constructed with this as the source point.

Based on the identification of ecological source sites, the center points of the main ecological source sites are taken as the ecological source point, and based on the ecological source points and resistance surfaces, the minimum consumption path from each source point to other source points is obtained, and subsequently, the minimum consumption paths between all points are superimposed to generate the ecological corridors between all source nodes, and then the critical corridors and general corridors are filtered out by the gravity model (

Table 7. Interaction matrix of the ecological source based on gravity model.

	Source Point 1	Source Point 2	Source Point 3	Source Point 4	Source Point 5	Source Point 6
Source point 1		5.99	4.16	1.31	1.35	0.42
Source point 2			28.80	5.75	4.31	0.75
Source point 3				7.67	9.23	1.13
Source point 4					7.73	1.33
Source point 5						2.13
Source point 6

).

There are nine ecological corridors in the Ningyuan County, with a total length of 216.87 km, including five important ecological corridors with a length of 96 km and four general ecological corridors with a length of 120.87 km (Figure 6). The nine corridors form a circular closed area, connecting Ningyuan County with each other and linking the southeast and northwest of the county. Sources 2, 3, and 5 have the highest gravity value among the six ecological sources. The interrelationship between Source 2 and 3 is the strongest, and the exchange and transmission of material and energy between the source areas are simpler, so, the ecological corridor is the most necessary, and the protection of these source areas must be strengthened to avoid destruction. The other sources are less connected and can be used as potential corridors. Potential corridors are more important to ensure the integrity and connectivity of the pattern, the impact on resistance is slightly higher than that of key corridors, and they are more affected and threatened by human activities.

Ecological corridors of different widths play different ecological service functions [40]; the corridors were analyzed according to existing studies for buffer areas with widths of 12 m, 30 m, 60 m, 100 m, 200 m, 600 m, and 1200 m [41], and the area share of land use types within each width were statistically analyzed (Figure 7). Woodland is the main land use type, and there are more than 2000 species of forest plants and 22 species of state-protected wildlife in Ningyuan County. Woodland is an important habitat for species and has a significant impact on species migration and exchange, followed by grassland. With the increasing width of the corridor, the proportion of forest land gradually decreases, while grassland and water area as a whole show an increase. The construction of ecological corridors should meet the conditions of low human activity interference and concentration of ecological land. Within the width range of 12–30 m, three types of ecological land, namely forest land, grassland, and water, have the highest proportion, and the proportion of land most disturbed by human activity, such as arable land and construction land, is at a low level. Within the 30 m width of the corridor, the proportion of construction land is the lowest, only 0.1%. Thus, the optimal width of the corridor should be 12–30 m.

Within the 30 m width, the dominant land use type of each corridor is woodland, which accounts for more than 80% of the area, followed by arable land and grassland, with less water and construction land (

Table 8. Land use of ecological corridors within 30 m width.

Corridor	Length(km)	Properties	Area of each Land Use Type (hm²)
			Woodland	Grassland	Waters	Cultivated Land	Construction Land
1–2	23.52	Important	60.57	0.63	0.18	1.08	0.00
1–3	29.53	General	71.64	0.99	0.27	5.13	0.09
2–3	12.87	Important	30.87	0.54	0.18	0.72	0.00
2–4	19.09	General	41.49	2.25	0.09	6.03	0.00
3–4	19.05	Important	36.18	1.62	0.63	8.19	0.00
3–5	22.76	Important	58.14	0.27	0.18	1.08	0.00
4–5	17.81	Important	33.03	1.98	0.00	11.88	0.00
4–6	33.82	General	79.47	5.85	0.09	3.69	0.00
5–6	38.42	General	89.64	3.51	0.63	7.56	0.00

). Ecological corridors in Ningyuan County guarantee the connectivity between ecological sources and are mainly distributed along woodlands and grasslands and pass through most of the nature reserves, basically avoiding non-ecological use areas. According to the plan for ecological restoration of land space in Ningyuan County (2021–2035), there are three major ecological restoration zones in Ningyuan County, namely the northwestern forest ecological protection and restoration zone, Leng Shui–Chung Shui watershed comprehensive land improvement and restoration zone, and the Jiuyishan water conservation and biodiversity protection and ecological restoration zone. The nine ecological corridors run through and connect the three major ecological restoration areas by linking ecological patches of mountains, forests, and fields, enhancing the functional integrity of the overall ecosystem.

4. Discussion

The paper integrates ecological sensitivity and ecosystem service value to determine ecological source sites, which avoids subjective interference in the method; the method of constructing ecological corridors through the minimum cumulative resistance model is widely used by domestic and foreign authors and has a certain degree of scientificity [42,43,44].

It quantitatively analyzes the importance of ecosystem services, ecological sensitivity, and the impact of land use types on ecological environment in Ningyuan County, thus scientifically identifying ecological sources and corridors and providing a basis for the construction of ecological security in Ningyuan County. The distribution patterns of ecosystem service values and ecological sensitivity are similar. Areas close to human production and living places are less ecologically sensitive, and areas far from human production and living places are more ecologically sensitive; areas with high ecosystem service values are mainly located in areas with better ecological quality, such as woodlands and waterways. The overall importance of ecological protection in Ningyuan County is high, with obvious spatial aggregation and divergence characteristics, and an overall spatial pattern of being high in the north and south and low in the central and western parts of the county, which is similar to the study by Li Long et al. (2020) [17]. The total area of ecological source land in Ningyuan County is 879.14 km², accounting for 35.15% of the county area. It is mainly distributed in the high-value ecological demand areas such as Wulongshan, Tongmuluo, Mianhuaping, Zhonghe, Shuishi, and Jiuyi. The spatial overlay of the three zones and three lines in Ningyuan County with the identified ecological source areas shows that the ecological space requiring key protection, such as the ecological protection red line and national nature reserve in Ningyuan County, is basically located within the source areas. The overlay of ecological source sites and ecological protection importance level layer shows that 88.32% of ecological source sites overlap with ecologically very important and important areas, indicating that the method adopted in this study is reliable and can scientifically identify important ecological protection areas in Ningyuan County, which can provide a reference for county ecological space protection and territorial space planning, guaranteeing regional ecological security.

Some of Ningyuan’s regional roads pass through areas of high ecological conservation importance or sensitivity. While enhancing regional transport links, they inevitably form a fragmentation of ecosystem integrity and destroy the habitat and breeding environment for wildlife. It is important to enhance habitat connectivity and optimize the spatial system of biodiversity conservation through the construction of ecological corridors. Therefore, this study is necessary.

Different species have different requirements for ecological corridors, and most areas of karst landscapes have a high degree of ecological sensitivity, so it is difficult to build an ecological corridor system. The analysis of widths is not sufficient and only considers land use types within buffer zones of different widths, without targeting the specific resistance relationships for species migration, and the width of a 15–30 m interval range obtained from the analysis leads to the generation of results that can only be used as a generalized pathway. In addition, attention should be paid during the planning and design process to determine whether the land use types within the corridor meet the relevant regulations of the natural resources department, for example, whether they encroach on prohibited development areas. These will create uncertainty in the implementation of specific construction. Moreover, this paper has not further articulated the territorial spatial planning system after the construction of potential corridors. In the future, the ecological security pattern of Ningyuan County can be further optimized and a multi-scale mosaic and integrated ecological network system can be constructed. For karst areas with complex and sensitive ecological environments, the ecological importance evaluation mostly focuses on natural and socio-economic evaluation factors. Ningyuan is a place inhabited by ethnic minorities, with a long history of Yao people, and the county government attaches great importance to ethnic work. In the follow-up study, humanistic factors should be considered, and the coupling analysis of socio-economic development and regional ecological security should be further studied by combining regional industrial development and the humanistic background.

5. Conclusions

Ningyuan County, Hunan Province, was the study area for identifying ecological source sites based on the results of ecological sensitivity evaluation and ecosystem service value calculation. Based on the MCR model and the least-cost path method, an ecological corridor system can be constructed by removing redundancy. The construction of nine ecological corridors will enhance the level of connectivity of ecological source sites in Ningyuan County, improve the habitat suitability of patches, and promote the migration and spread of species. Hence, using this method to realize the ecological corridor system is of great significance in protecting the biodiversity and improving the quality of the ecological environment in Ningyuan County.

In the future, information such as biological data and relevant regulations of natural resource departments could be collected and analyzed, while considering human factors, such as combining regional development and the ethnic minority background, so as to study the rationality of corridor construction in depth, articulate a good territorial spatial planning system, further construct an ecological security pattern, and build a multi-scale ecological network system.